2-Dimensional and 3-Dimensional Carbon Structures for Hydrogen Storage

Abstract

An ever-increasing global focus on sustainable practices has led scientists to explore hydrogen as a fuel source [1-12]. As the most abundant element in the universe, diatomic hydrogen gas can be combusted to produce energy and water as biproducts. The main hinderance to a widespread hydrogen economy is difficulty in storing the dangerous gas. Currently the two most common ways to store hydrogen are in compressed gas tanks and in refrigerated tanks as a liquid. A less common method of storing hydrogen is via causing other materials to absorb the gas within their chemical structure through a process known as physisorption.Carbon based materials are highly promising for sustainable chemistry as they are typically cheap to produce, and some studies have already begun to explore their ability to aid in hydrogen generation reactions.This study aims to compare the ability of two carbon-based materials, graphite flakes and graphene, to adsorb hydrogen gas. Graphene as two-dimensional (2-D) structure was chosen for its well-known high surface area. Graphite flakes as three-dimensional (3-D) structure were chosen for comparison as they are a precursor in the synthesis of graphene. Micromeritics ASAP 2020 was used to determine the hydrogen uptake of the two materials. Volumetric hydrogen adsorption isotherms were measured at 77 K and up to 1 bar. Hydrogen gas sorption isotherms were obtained using ultra-high purity grade (99.999%) gas. Before analysis, the pre-treated samples (0.2000 g) were outgassed in the analysis tube under vacuum (down to 10-7 bar) with heating up to 120 °C, which is sufficient to remove solvent molecules without thermal decomposition or loss of samples integrity. The adsorption study indicated that graphene had a weight percent adsorbed of 16 %H₂/g while graphite flakes only had a weight percent adsorbed of 7 %H₂/g. It is likely that the higher surface area of graphene allowed it to adsorb more hydrogen gas than the graphite flakes. This study gives some insight into different materials and their hydrogen adsorption capability. Future work could explore more materials to determine which is the best for hydrogen storage.